The Mainz Cathedral
When History Hangs in the Air – A Glimpse into Its Chemical Scent Signature
The indoor air was collected using sorptive materials and later analyzed in the laboratory with thermal desorption and gas chromatography–mass spectrometry (TD-GC-MS). (Photo: Alexandra Gutmann)
The Mainz Cathedral is not only an impressive building of historical and cultural importance but also a unique space for investigation. The air inside such a structure carries the traces of its materials, its history, and its use. Old wood, masonry, paints, restoration materials, but also candle smoke, incense, or visitor activities leave behind volatile substances that can be detected with sensitive measuring techniques.
This distinctive fragrance makes the cathedral an ideal subject for our project. As part of our project D2Smell, we recorded an emission spectrum inside the Cathedral. The aim is to use chemical analysis to understand which organic compounds are present in the indoor air—and what they can tell us about the past and present of this place.
Emission Spectrum of the Mainz Cathedral
The chromatogram below shows the composition of the volatile organic compounds (VOCs) detected in the Cathedral’s indoor air. Unlike floral scents, these substances originate from a wide variety of sources: building materials, organic aging processes, cleaning agents, candles, or liturgical fragrances such as incense.
Depiction of the volatile organic compounds (VOCs) found in the Cathedral’s indoor air. The peaks represent individual substances—aldehydic, aromatic, and terpenoid compounds. (Measurement and processing: Kathleen Raap)
We were able to identify a series of characteristic substances that allow conclusions about their sources:
🪵 Furfural & Hexanal
These two aldehydes are formed during the aging of wood or textiles and point to historical building materials or furnishings inside the Cathedral. They are typical markers of organic decomposition processes of wooden interiors.
🌼 α-Pinene & Nonanal
Two substances that reflect everyday life inside the Cathedral. α-Pinene is a characteristic monoterpene of coniferous wood and resins, also present in incense. Its fresh, resinous scent recalls a pine forest and lingers in the indoor air longer than most other terpenes. Nonanal, on the other hand, carries a waxy, citrus-like odor and can arise both from the degradation of organic materials and from perfume oils—or even from the presence of people themselves.
🕯️ Decane
Candlelight leaves behind more than just brightness — it also leaves traces in the air. Decane is a long-chain alkane found in paraffin products such as candles and waxes. It is hardly noticeable by smell, but it contributes a subtle “warm” base note.
🎨 Xylole & Ethylbenzol
These aromatic compounds usually originate from paints, varnishes, and adhesives. They point to restoration work or to older coatings that still release small amounts of volatile substances. They may also be produced by candle burning.
🧴 Acetic Acid
A simple yet striking compound, sharply sour and unmistakably vinegar-like. While we collected our samples early in the morning, cleaning was already underway elsewhere in the cathedral. Although we did not perceive the smell at our measuring spot, our instruments certainly did. Acetic acid, however, does not only come from cleaning agents – it is also emitted by humans through breath and skin. What we captured may therefore have been the subtle remains of the visitors from the previous day. Learn more on our project page on human scent emissions.
The presence of these substances in the Cathedral’s air is a chemical expression of lived practice. Over the years they have inscribed themselves into the interior—like an invisible record. They reveal what has taken place there and give the Mainz Cathedral its own unmistakable scent.
Text: Alexandra Gutmann